Abstract: The 300M steel test plate was prepared by using laser-cladding XF-G01 powders in X groove. The microstructure, microhardness and the micro-regional chemical composition were further examined by means of optical microscopy, micro-hardness tester, scanning electron microscopy and X-ray diffraction spectrometry (EDS). Moreover, the mechanical properties of the test plate and the 300M steel were also compared and investigated. The results show that the cladding layer of the test plate near the matrix exhibits a fast-cooling cellular microstructure, while the microstructure of the parent metal is composed of lath martensite and a trace of bainite. The average microhardness of the cladding layer is about 400 HV, while the microhardness of the cladding layer which is 0.3 mm near the matrix significantly increases to 595 HV due to obvious composition gradient.Meanwhile, the width of heat-affected zone is about 0.2 mm with the microhardness of 695 HV. The microhardness of the parental metal is about 705 HV. Because of the composition gradient at the interface position between the cladding layer and the matrix, the mechanical properties of the cladding layer and the matrix material can match well which makes the test plate have better strength and toughness matching.The average ultimate tensile strength of the test plate is 1600 MPa, the average impact toughness is 81 J/cm² and the average fatigue cycle is 42904. Both the toughness and fatigue property of the laser-cladding test plate is superior than those of the 300M steel except for the relatively lower ultimate tensile strength.